Process for heat treatment of metallic strings for stringed instruments

ABSTRACT

A string of a stringed instrument is heat treated to a temperature less than its annealing or softening temperature under tensile stress to reduce residual stress in the string and thereby minimize tonal variation over long periods of time after the string has been strung in the instrument. The string is electrically heated, optionally after stringing in the instrument. The tensile stress is 40-160 kg/mm2 and the heating temperature is 150*-400*C.

United States Patent 91 Fukuda Aug. 21, 1973 PROCESS FOR HEAT TREATMENT OF METALLIC STRINGS FOR STRINGED INSTRUMENTS [75] inventor: Hiroshi Fukuda, lwata, Japan [73] Assignee: Kabushiki Kaisha Katvai Gaklti Seisakusho, Shizuoka-ken, Japan 221 Filed: July 26,1971 [21] App]. No.: 165,895

[30] Foreign Application Priority Data July 27, 1970 Japan 45/65875 Apr. 8, 1971 Japan..., 46/2201! [52] US. Cl 148/131, 84/199, 148/13, 148/156, 219/58 [51] Int. Cl C2ld 9/52 [58] Field of Search 148/12, 11.5, 154,

[56] References Cited UNITED STATES PATENTS 3,196,052 7/1965 Hann 148/12 2,281,132 4/1942 Young 148/12 2,932,502 4/1960 Rudd et a1. 148/156 X 3,068,353 12/1962. Hann et al. 219/155 3,580,746 5/1971 Behar 148/12 3,469,829 9/1969 Fujita et a1 148/156 X Primary Examiner-Charles N. Lovell Attorney-Eric l-l. Waters et a1.

[5 7] ABSTRACT 6 Claims, 6 Drawing Figures PATENIED AIIBZI I818 SHEEI 2 0F 6 5 5:; wE mczmwr Internal Residual Stress (Kg/mm?) INVENTOR 7M iwa,

Mariam-a1 ms 31753797 SHEH 3 BF 6 Lapse of Time (hrs.)

Musical Step Lowering Degree ht) INVENTOR PAIENIEBAMZI nan SHEEI h 0F 6 UL E EwQEm 053m; 03 0% QR 0Q Musical Step Lowering Degree (g nt) INVENTOR PATENTED M1221 I975 SHEET 5 [IF 6 v INVENTOR W'XM PROCESS-FORIHEAT TREATMENT OF METALLIC STRINGS FOR STRINGED' INSTRUMENTS BR'IEFSUMMARY OF THE INVENTION This invention relates-to a process for the heat treatment of ametallic string for a stringed'instrum'ent suchas a piano or the like.

It has been usual hitherto to produce apiano string of a desired'diameter from steel, such as a carbon steel, by effecting a heating treatment and a wire drawing operation, successively.

The'piano stringthus obtained has a satisfactorytensile strength; If, however, the string is installed in'a piano under atensile stress of 100-180 kg/mmand is leftas is for a long period of time, the tensilestress is relievedto cause loweringof the musical tone or step thereof. The upper portion'in FIG. l shows this condition. Namely, the change of themusical step of each stringtwo months after stringing-is shown therein. It will be-clear therefrom that the musical tone or step of each string is'lowered -30 percent from the initial musical step at the timeof stringing as shown byblack dots.- The average'thereof is about 1 8 percent, and eventhough considering. a range of i 5' percent therefrom (thisrange is'considered to beone in which a generally trained: person cannot detect the difference by'hearing), thereare still some strings which are. outside this range; It is almost impossiblexto hold. the variation withina range of i 3percent (thisrange is considered to beoneiin'which a-specially trained person CflI'IIIOtxdC- tect the difference by hearing).

One of the causesof the changeiin musical value is considered to. originate in the'internal-residual stress causedat the-time of wire drawing. Heretofore, a heat treatmentat a temperature lower than anannealing andsofteningtemperature under! no tension has been carried out for removing this internal residual; stress,

but only about .20-30 percent of the internal. residual stress is removed. Accordingly, theloweringof'the musical tone of the string afterstringing thereof has shown' a large valuesimilar to anuntreated string. I

An object of this invention is to provide a process for' heat treatment of a string wherebysthe internalresidual stress is removed'andthe lowering of the musical value is not brought about even over a long period of time after stringing. I

The invention is characterized in that a metallic string obtained by-a wire drawing operation is heated.

to atemperature lower than the annealingand softening temperature. while being subjected to astensile stress.

BRIEF DESCRIPTION OF THE DRAWING FIG. 6 is a side elevational view, partly in crosssection, of another embodiment according to this invention.

DETAILED DESCRIPTION Four piano strings A,B,C, Dare prepared, andare. heated at a temperature of 300C below the annealing and softeningtemperature thereof under conditions in by the foregoingprocess are strung, under a tension stressof kg/mm and at thesam'e time'asconventional string-,E which has not been subjectedv to heat treatment is similarly. strung. The degree:of lowering of the musical tone during lapse of time is measuredand;

the results are plotted inFIG. 3. ln comparison with thestringE (not subjectedto heattreatment), the.string-A'- subjected to a heat treatment under. no tension, and the strings B, C, D' gradually increased: in .tensilestress, are generally reduced. in the degree of lowering of the musical tone.

Considering thetuningoperation, which-is the last.-

stage ofa conventional piano. manufacturing, process this requiresseveraltensof hours from the. initial-.tun-

ing step to the-completion tuning step. The.lowering';of

musical tone during. this tuning operationv does'not cause great problems because the-tone. isadjustedxinv the completion tuning step;

Considering this fact, substantialsignificance lies in the period. subsequent to the lapse of the several tens I of hours; FIG. 3 shows that the loweringof'the'toneof string E between 20-] ,000. hours isZO percent, while that of stringpA'is morexthanlO percent. The strings B, C, D-' subjectedfto the heat treatmentofthis'invention, have extremely small loweringof tonal valuesand. these-are k.- 1/10 in comparison with strings A and;

E. The string:.D. is especially excellent. Accordingly; retuning afterthe lasttuningstepis not required for-the. strings which have been treated accordingtotheinvenxtion.

FIG. 4 shows the relation.between the.treatmenttenfperature andthe degreeoflowering of themusical tone:- 20-1 ,000 hoursiafter stringing a string A""subjected to. no tension. stress and.strings.B",.C.", D' subjectedto tension stressesv of I 42, 84 and 12.6 kglmm; respec tively. As for the..lowering of the musical valuesduring this. time, up to'about 13 percent is permissible.Ac?-- I cordingly, the heat treatment temperature may be from. about l50 C to-about 400C'within thezrangezof. tensile stress'of$40-i00-kg/mm g I The. lower. portion in FIG. 1 refers to piano-strings each heat treated for'l minuteiat 300 C'undera.tensile. stress of IOOkg/mmiand strung in a.piano andthedegree-oflowering, of ithe' musicaltonal. values after two I months is illustrated.Theaverage degree of loweringgi'sa' 7'percent, and therange'of' this changemay berheld. within about i 3 percent. (this range is the. rangeain:

which a person having a high auditory sense cannot tell the difference by hearing).

Thus, a piano string treated in accordance with this invention, has a very small degree of lowering of musical tone even over a long lapse of time after stringing in comparison with a conventional string. Consequently, the number of tuning steps required may be substantially decreased. Furthermore, the dispersion of the lowering degree is narrow and thus the tone can be maintained for a long time.

An oxide coating is formed on the surface of the string to prevent rusting thereof.

The process of the invention is effective not only for high carbon steel strings but also for stainless steel strings, phosphor bronze strings and others. Additionally, the strings of this invention are not limited to use in a piano but are applicable to any other stringed instruments.

FIG. shows the apparatus for effecting the process of the invention treatment. Therein, a steel string a is fixed at one end to an electrically insulated clip la and passes over a guide roller 2 and is fixed at its other end to a clip lb mounted on a lever 5 supported at one end by an axle 3 and carrying a weight 4 at its other end. Consequently, a tensile stress is produced in string a by the weight 4. Terminals 7 are connected to an electrical source 6 and are connected to string a at spaced locations thereon so that a predetermined electrical current flows through the string for apredetermined length of time under the control of a time-limit relay 8. Numeral 9 denotes a voltage regulator and numeral 10 denotes a voltmeter. Numeral ll designates a cover for the string a to permit the string to be heated uniformly while being isolated from air flow. In a modification, the string a can be a long continuous string as shown by dotted lines and it is moved step by step for each unit length of the final string to be obtained FIG. 6 shows an embodiment wherein the string a is heated by electrical current flow in a condition in which the string has been actually strung in a piano. Namely, a tuning pin 12 is driven in a wooden tuning pin plate 13 and thereby is electrically insulated from a sound plate 14 and a back 15, and is also insulated from a frame 16 by a bushing 17, the string a being strung between the foregoing tuning pin 12 and a hitch pin 18 while being subjected to a tensile stress of kg/cm. An insulating material 20 is interposed between the string and a pillow 19 so that the string a becomes completely electrically isolated. Numeral 2] denotes a bridge which is an electrical insulator. Terminals 7 connected to an electric source 6 are connected to both ends of the string a and a predetermined electrical current is passed therethrough for a predetermined length of time under the control of time-limit replay 8. Thus, the string a which has an electrical resistance of 0.1 to 0.4 film is heated. The heating temperature thereof is set within the foregoing range of i50400C.

In the illustrated embodiment of FIG. 6, it is not only possible to heat a single string a, but it is also possible to heat several strings simultaneously.

What is claimed is:

l. A process for heat treatment of a piano wire pro duced of a wire from the class consisting of high carbon steels, stainless steels and phosphor bronze, said process comprising heating said piano wire to a temperature of l50-400C which is lower than its annealing and softening temperature while simultaneously subjecting the piano wire to a tensile stress of 40-160 Kg/mm for a relatively short period of time so as to reduce the degree of tonal reduction of the piano wire to a value of no more than about 13 percent after about 2,000 hours after the piano wire has been strung in the instrument.

2. A process as claimed in claim 1 wherein the string is subjected to tensile stress by fixing the string at one end and applying a weight to its opposite end and the string is heated by passing an electrical current through an intermediate portion of its length.

3. A process as claimed in claim 1 comprising mounting the string in the piano before it is heated under tensile stress.

4. A process as claimed in claim 3 wherein the string is mounted in the piano by being connected to a tuning pin and a hitch pin, the piano wire being heated by passage of electrical current therethrough.

5. A process as claimed in claim 4 comprising electrically isolating the string in said instrument.

6. A process as claimed in claim I wherein the string is heat treated for 1 minute. 

2. A process as claimed in claim 1 wherein the string is subjected to tensile stress by fixing the string at one end and applying a weight to its opposite end and the string is heated by passing an electrical current through an intermediate portion of its length.
 3. A process as claimed in claim 1 comprising mounting the string in the piano before it is heated under tensile stress.
 4. A process as claimed in claim 3 wherein the string is mounted in the piano by being connected to a tuning pin and a hitch pin, the piano wire being heated by passage of electrical current therethrough.
 5. A process as claimed in claim 4 comprising electrically isolating the string in said instrument.
 6. A process as claimed in claim 1 wherein the string is heat treated for 1 minute. 